1. Field of the Invention
The application relates to thermally operated valves and in particular, to valves utilizing temperature expansion of a gas to move a valve closing member.
2. Description of the Prior Art
The prior art, as exemplified by U.S. Pat. No. 2,627,911, No. 2,787,130 and No. 3,405,999, contains many thermally operated valves including valves utilizing gas charges with adsorbent activated carbon materials, such as activated charcoal, for operating valve closing members. Attempts to manufacture such activated adsorbent material containing valves in quantity have generally met with failure; activated carbon materials generally do not produce sufficient increase in volume or pressure change per degree change in temperature to warrant the added cost of the carbon materials; and different batches of activated materials exhibit widely varying adsorbent properties which make reliable manufacture of valves to be operated at a predetermined temperature impractical. Some valves require a significant degree of movement of a valve closing member to operate properly, particularly flame responsive valves in gas fired appliances and only liquid-vapor actuators, such as mercury actuators, could produce the amount of pressure or volume change per degree of temperature change necessary to produce sufficient valve member movement; however, such liquid vapor valves are limited to operation at temperatures near the boiling point of the liquid.
Also, the prior art, as exemplified in U.S. Pat. No. 1,744,735, No. 3,258,363; No. 3,442,819; No. 3,516,791 and publication (USSR Academy of Science, M. M. Dubinin, "Thermal Treatment and Microporous Structure of Carbonaceous Adsorbents" Proceedings of the Fifth Conference on Carbon, Volume 1, 1962, pages 81-87), contains many adsorbent carbon materials including decomposed polyvinylidene chloride and polyvinylidene fluoride. Adsorbent carbon materials are widely used in removing contaminants, or the like, from gases or liquids. Polyvinylidene chloride and polyvinylidene fluoride, in particular, have been recognized for their "molecular sieve" property, that is, their ability to adsorb certain gaseous materials which have small molecular sizes while being incapable of adsorbing other gaseous materials which have larger molecular sizes.